The invention relates to a disc cassette for use in a system for storing/reading information.
U.S. Pat. No. 4,239,238 (herewith incorporated by reference) discloses a cassette of the type comprising an external enclosure and a closing member received therein. The enclosure has parallel main walls, three side walls, and a front opening which communicates with a disc receiving space. The closing member is situated partly inside and partly outside the enclosure and closes the front opening. A latching finger on the closing member cooperates with a recess in a main wall of the enclosure to hold the closing member in the enclosure. The known disc cassette contains a video disc provided with video information which is stored in the disc in the form of geometrical variations in the bottom of a continuous spiral groove formed on the disc surface. The variations in the capacitance between an electrode of a stylus which slides in the grooves and an electrically conductive layer on the surface of the disc are detected in order to reproduce the stored information. Such a video-disc system based on capacitance variations is described comprehensively in U.S. Pat. No. 3,842,194 (herewith incorporated by reference).
In such systems it is advantageous to accommodate the disc in a cassette having an enclosure which is closed by means of a closing member provided with a disc extractor in the form of a plastic strip which surrounds the periphery of the disc with clearance. To play the disc, a cassette containing the disc is inserted into a playing apparatus having a disc-extraction mechanism which removes the disc from the enclosure during the subsequent withdrawal of the enclosure, so that the disc remains in the player. The player is equipped with a turntable which supports the disc for the subsequent playing operation. After playing the empty enclosure is reinserted into the player and is subsequently removed from the player together with the disc and the closing member. Discextration mechanisms suitable for cooperation with such disc cassettes are known, for example, from U.S. Pat. Nos. 4,089,511, 4,421,866 and 4,133,540.
It is desirable to ensure that a disc contained in an enclosure cannot inadvertently fall out of the enclosure. Further, it is desirable that the closing member cannot readily be removed from the enclosure outside the apparatus. Therefore, the closing member comprises pivotal latching fingers which in conjunction with the latching recesses formed inside the enclosure effectively latch the closing member in the enclosure. When a filled disc cassette is inserted into the player the latching fingers are pivoted to their released positions. This enables the closing member to be removed and hence the disc to be removed from the enclosure inside an apparatus.
U.S. Pat. No. 4,352,174 (herewith incorporated by reference). Discloses a disc cassette provided with a video disc which must be scanned capacitively but which is not grooved. Like the video disc mentioned in the foregoing this disc must also be protected against dust and touching. Therefore, the disc is again accommodated in an enclosure, which is closed by a closing member which is latched in the enclosure by means of latching fingers. The disc cassette is inserted into a player, after which the closing member is released by suitable means provided in the player and is removed from the enclosure together with the disc during withdrawal of the enclosure from the player. The disc and the closing member can be reinserted into the enclosure by sliding the enclosure into the player, so that the disc with the closing member are replaced and the closing member is latched in the enclosure. The closing member is not provided with disc-extraction means. The player is equipped with an extraction mechanism which slightly opens the enclosure of a disc cassette inserted into the player and grips the edge of the disc around the closing member by means of a gripper. This enables the disc and the closing member to be simultaneously withdrawn from the enclosure.
Protection against touching, dust and environmental influences is not only desirable for capacitively scanned video discs but also for various other types of disc. In general, these are discs of a type on which information is stored with a very high density, necessitating a very accurate scanning of the disc surface. This category not only includes video discs but also magnetic storage discs, optical audio discs and video discs, as well as optically readable computer storage discs of the recordable or non-recordable type. Despite the extremely high information density normal optical audio and video discs do not employ disc cassettes. However, the player comprises electronic correction circuits which synthesize the missing information in the event that the information structure cannot be read owing to the presence of dust or the like. In the case of optically readable storage discs in which each information element may be essential such corrections are permissible only to a limited extend. In the event that reading of the information is locally impaired by the presence of dust, scratches, fingermarks or other flaws, this may have undesirable and sometimes even serious consequences.
The prior art also teaches disc cassettes in which the disc is not removed from the enclosure but remains in the enclosure in order to be scanned by the player. The enclosure should provide enough room and should have apertures which can be closed and which provide access to the disc surface for the customary scanning means. Therefore, such disc cassettes have larger dimensions and require the presence in the player of means for opening the access slot which can be closed and, in some cases, the central opening for the passage of a drive spindle.
In most disc cassettes known from the above United States Patent Specifications the latching fingers are situated on the two lateral sides of the closing member. The latching fingers pivot in the plane of the closing member and the associated latching recesses are provided in the corresponding lateral side walls of the enclosure. Near the side walls apertures are formed in the front side of the closing member, through which apertures release means of the disc player can enter the enclosure to bend the latching fingers towards their released positions. The gripping means in the player engage around the portion of the closing member which projects from the enclosure, after which the enclosure can be withdrawn, leaving the closing member and the disc behind. Care must be taken that when the enclosure is reinserted into the player the latching means no longer keep the latching fingers of the closing member in their released positions, because otherwise the closing member is not latched in the enclosure and consequently the enclosure cannot take up the closing member and the disc. The release means of the disc players are therefore constructed in such a way that during or after withdrawal of the enclosure the release means are set to another position, so that these means no longer load the latching fingers are not disposed in the path of an enclosure to be inserted subsequently.
However, the first-mentioned U.S. Pat. No. 4,239,238 also describes a construction of a disc cassette in which the latching fingers are not arranged on the lateral sides of the closing member to cooperate with latching recesses in the lateral side walls of the enclosure, but in which the latching fingers are disposed substantially within the plane of the closing member and are pivotable in a direction perpendicular thereto to cooperate with latching recesses in a main wall of the enclosure. For pivoting the two latching fingers and for subsequently withdrawing the closing member and the disc from the enclosure the disc player employs a combined release and extraction means which penetrates into the front opening of the enclosure. The latching finger extends into the front opening and at this location it comprises a hook-shaped portion. The latching member of the disc player pivots the latching fingers towards the released positions and also engages behind the hook-shaped portion to withdraw the disc holder with the disc from the enclosure. After removal of the enclosure the latching finger pivots back elastically and thereby pivots the release and extraction means of the disc player into an inoperative position. This enables the closing member to be reinserted and latched in the enclosure. A disadvantage of this cycle of operations is that during the release and withdrawal of the closing member from the enclosure the latching fingers are pivoted against spring force and a reactive force is exerted on the facing main wall of the enclosure. This force gives rise to the front side being bent open and may lead to permanent deformation and damaging of the enclosure. This is induced by the fact that the main wall is locally bevelled towards the front opening down to a very small wall thickness. The latching finger may be made less rigid but this renders the finger more vulnerable. This construction is not very suitable for further miniaturisation, because the problem will then become even more serious. Another disadvantage is that the hook-shaped portion of the latching finger is necessarily small. Nevertheless this hook-shaped portion has to be subjected to the force required for withdrawing the disc with the closing member from the enclosure. Under unfavourable conditions this may give rise to damaging or rapid wear of the hook-shaped portion, thereby rendering the disc cassette unserviceable. Such unfavourable conditions may occur if the closing member and/or the disc jam in the enclosure, for example, as a result of deformation of this enclosure. Another disadvantage is that the latching fingers have a double function, because they serve both for latching the closing member in the enclosure and for withdrawing the closing member from the enclosure. It is not always desirable that such a part performs more than one function and it may be more advantageous to optimise this part for only one function. Other functions impose different requirements, so that a part which serves several functions cannot always be optimised in all respects.
In all disc cassettes of the type described, in which the closing member is removed from the enclosure after it has been released, openings are necessarily at the front side of the closing member for the passage of release means of the apparatus. Gripping means grip around the portion of the closing member which projects from the enclosure-or at least a part thereof-in order to withdraw the closing member from the enclosure, except in the construction of a disc cassette where the latching finger is pulled.